This decision forced some crew shuffling; NASA had to take two astronauts off the originally four-person Crew-9 launch to make room for Wilmore and Williams on the downward leg. (Both Starliner astronauts are in good health on the ISS, and there are plenty of supplies to support them through the end of their stay, NASA officials have said.)

While Suni Williams and Butch Wilmore’s situation is unusual, their return trip will be pretty routine, as they were already slated to fly home on a SpaceX capsule as part of a scheduled crew rotation.